TABLE OF CONTENTS Forming processes commonly used to manufacture tubes and pipes often induce some yield anisotropy in the finished products. Such anisotropy affects the collapse pressure and other limit states of pipelines. The anisotropy must thus be determined and included in the modeling of the various limit states. Hill-type anisotropy [B.1] is usually adequate for modeling the yield characteristics of tubes. For commonly-used pipe dimensions, a state of "plane" stress usually suffices. The yield function in terms of polar cylindrical coordinate stress components can be written as
| (B.1) |  |
where S ? = ? o?/ ? ox, S r = ? or/ ? ox, S x? = ? ox?/ ? ox, { ? ox, ? or, ? o?} are the yield stresses in the respective directions (axial, through-thickness and circumferential), and ? ox? is the yield stress under pure shear.
Four experiments are required to establish the anisotropy constants in (B.1). For larger diameter and relatively thick tubes, the mechanical properties in the three normal directions can be measured directly on test coupons extracted from each direction. The shear anisotropy requires an independent shear test. For smaller diameter tubes, the following experimental procedure has been found to be effective [B.2].
Two of the material constants can be evaluated directly by measuring the uniaxial stress-strain response in the axial and circumferential directions. In the axial direction, the response is measured from a uniaxial test on an axial...
